Portable fluorescent lamp



Feb. 2, 1954 H. AKROYD I 2,668,229

PORTABLE FLUORESCENT LAMP Filed Nov. 23, 1948 ggenio Attorney 3 Sheets-Sheet 1 F 5 H. AKROY D PORTABLE FLUORESCENT LAMP 5 Sheets-Sheet 2 Filed Nov. 25, 1948 Inventor A tto ney H. AKROYD PORTABLE FLUORESCENT LAMP :5 She ets-Sheet 5 TT T w Inventor flaflazzi/nvvf Attorney Feb. 2, 1954 Filgd Nov. 25, 1948 hi vb Patented Feb. 2, 1954 PORTABLE FLUORESCENT LAMP Harold Akroyd, Denton, land, assignor to Old Denton, near Manchester,

company near Manchester, Engham and Son Limited,

England, a British Application November 23, 1948, Serial No. 61,560 Claims. (01. 24010.6)

This invention relates to fluorescent lamps.

A main object of the invention is to devise a means of operating a fluorescent lamp from an accumulator.

A further main object is a lighting unit embodying a fluorescent lamp supplied by an accumulator whichis adapted for use in coal mines.

The invention consists in means for operating a fluorescent electric lamp from a source of direct current of voltage substantially less than that required to operate the lamp, the means comprising in combination connections for the direct current supply, a vibratory make and break device for the current, a holder or holders for the lamp and a step-up transformer the primeans for operating mary winding of which is serially connected to the current interrupter and the connections for the direct current supply, and the secondary winding of which is connected to the said holder or holders for the lamp, the ratio of the transformer windings being such as to give a secondary voltage suflicient to start and operate the lamp.

The invention also consists in a transportable electric lighting unit which is substantially flameproof and employs a fluorescent lamp or lamps, the said unit comprising an accumulator or accumulators having sealed cells and giving a voltage substantially less than that required to operate the fluorescent lamp or lamps, and means according to the preceding paragraph, the said lamp or lamps, accumulator or accumulators and the said means being enclosed in a substantially flameproof casing provided with a window for emission of light from the lamp or lamps with terminals accessible outside the casing for recharging the cells and with openings venting the accumulator cells to atmosphere.

The fluorescent lamp circuit may be rendered stable in the usual way by chokes, resistances, or condensers, or alternatively, by a combination of these components.

Preferably, the accumulator is connected to the centre of the primary of the transformer, the two ends of the primary being connected to the two contacts respectively of the vibrator which are closed alternately, whereby the intermittent current is alternating.

Alternatively, two fluorescent lamps, each with a transformer, may be supplied with unidirectional intermittent current by connecting one poleiof the accumulator to the end of the primary of each transformer, and the other pole to the common contact of the vibrator, while the other ends of the primaries are connected to the two contacts of the vibrator which are closed alternately, thereby the intermittent current is supplied to the two lamps alternately, and, if the two lamps are close together, flickering is avoided.

In the case of lamps requiring preheating, the preheaters may be supplied from the secondary of the transformer or directly from the accumulator, being put into circuit by a starting switch which is opened as soon as the discharge starts.

In the usual commercial form of fluorescent lamp, the discharge terminals are in the form of cathodes and are adapted to be preheated. A typical 10 inch tube which has an operating voltage of about 54 volts, requires a striking voltage of about volts, while the preheating circuit requires a current of about double the tube cur rent at 54 volts.

According to the invention, for supplying a fluorescent lamp of this type, the transrormer is designed with a regulation characteristic of secondary volts falling rapidly with the. load, the voltage being the normal operating voltage at the load of the lamp, a high voltage adequate for striking at no load, and a low voltage adapted to the preheating circuit at the high load of the preheating circuit. A transformer with this characteristic W111 render the lamp circuit stable without the use of auxiliary choke or resistance.

The transformer is preferably given this characteristic by giving it high reactance, but alternatively, by introducing resistance into its windings or circuit.

The operating means for fluorescent lamp according to the invention comprises a main switch and a starting switch. The main switch closes ing magnet of the vibrator is in a shunt circuit from one contact to the accumulator. Thereby alternating current is supplied to the primary of the transformer. The secondary of the transformer is connected to the discharge terminals of the lamp which, in the said type of lamp, constitute one terminal of the cathode. The starting switch is adapted to close the preheating circuit of the cathode.

When the starting switch is closed, the high preheating load is put on the secondary and its voltage drops to the value required. When the opened, there is no load on the secondary, and its volts rise to the high voltage required for striking. As soon as the discharge starts putting a load on the transformer, its volts drop to normal operating volts.

During the useful period of discharge of a lead accumulator, the voltage falls substantially, for instance, from 2.2 to 1.8 volts per cell. This variation of voltage is more than is suited to proper operation of a fluorescent tube. A regulator, therefore, is included in the accumulator circuit, adapted to maintain an approximately constant current in the primary of the transformer while the accumulator voltage falls during its period of discharge. This regulator may be a barretter of usual type, employing an iron wire of which the resistance increases rapidly with temperature.

In order that the invention may be more clearly understood, reference will now be made to the accompanying drawings which show byway of example, preferred embodiments thereof and in which:

Fig. l is a diagram showing means for operating two fluorescent lamps operated from one accumulator through the intermediary of one vibrator;

Fig. 2 is a front elevation partly in section through line II-II of Fig. 3 of a transportable lighting unit suitable for use in atmospheres where there is danger of inflammation or explosion, especially in a coal mine;

Fig. 3 is a side elevation of the unit partly in section on line III-III of Fig. 2, and

Fig. 4 is a plan view of the unit with the left hand half of the top wall removed.

A current interrupter in the form of a vibrator 44 consisting of a reed I, fixed at one end to a block 2, carries at the other end an armature 3 adapted to vibrate before the pole-piece of the driving magnet 4. Contacts 5 on the reed are adapted to make contact alternately, as the reed vibrates, with the two fixed contacts 6. Quench circuits I bridge the contact gaps.

A 6 volt accumulator 8 is connected to the reed through a main switch 9 and a barretter I8. The soil of the magnet and to one of the fixed contacts 6. The other pole of the accumulator 8 is connected to the centre tap of the primary winding II of a transformer 4-3 associated with the lamp Li, the two fixed contacts 6 are connected, respectively to the two ends of the primary II, and the terminals of the secondary winding I3 are connected to the discharge terminals ii of the. lamp Li. The discharge terminals l5 are in the form of preheater cathodes, each with terminals Hi and it. The secondary is connected to the terminals it, while the terminals 16 are connected together through a contact 11 of a starting switch I8. A suitable condenser i2 is connected across the secondary winding [3 of the transformer to improve the operating characteristics of the transformer.

The circuit including the vibrator, the lamp LI, and the associated transformer 43 is duplicated from another pair of contacts on the same vibrator to incorporate the lamp L2.

To cause operation of the lamp Li a respective pair of movable contacts 50. are mounted on the reed in operative relation with fixed contacts Ea connected to the ends of the respective primary winding. Thetransformer and its primary winding associated with the lampLE and the respective secondary winding and condenser are indicated by the references 43a, I Ia, I3a and 42a respectively, the. cathodes I511 of the lamp L2 be- 4 is connected to the reed ing connected in circuit in manner identical with that described with reference to the lamp LI, the preheater circuit being controlled by contact I'la corresponding to the contact I! already referred to with reference to lamp Li.

The two fluorescent tubes indicated at Li and L2 are of identical design.

The circuits may be traced as follows: for normal operation, from the positive pole of the accumulator 8, through the main switch 9, the barretter it, the reed i, the pair of contacts 5, 6, to the left hand portion of primary II of the transformer associated with lamp LI and from the centre thereof to the other pole of the accumulator. At the next vibration of the reed, the circuit deviates through the other pair of contacts 5, 6, through the other half of the primary H.

The circuit through the driving magnet 4 is from the accumulator through main switch 9, through starter switch contacts I9 hereafter referred to, to the reed I and thence through the magnet coil to the primary of the transformer II, and back to the accumulator. This circuit is intermittent since the drive coil is short circuited when the left hand contacts 5, 6 (as viewed in the diagram) are closed.

On closing the main switch 9 current flows through the barretter ID, the reed I, and the driving magnet 5 through the left hand half of the primary winding II back to the accumulator, thus causing excitation of the driving magnet 4 and consequential vibration in the reed I. As a result of vibrating the reed I, the contact 5 en gages the left hand contact 6, thus the drive coil is short circuited and current flows through the left hand half of the primary winding inducing current in the associated secondary I3. Simultaneously, the contacts 5a engage the fixed contacts 6a, and current flows first through one half of the primary winding Ila inducing flow through its associated secondary I3, and in the next movement of the reed I, due to its own resiliency, the left hand contacts are opened and the right hand contacts 50, 6a are closed, causing the other half of each primary to be energised and simultaneously to short circuit the driving magnet 4.

The starting switch I8 is then operated and closes the two pairs of contacts I! and Ila thus closing the circuits through the preheating cathodes of the respective lamps Li and L2.

The barretter IQ is associated with the con,- tacts I9 of the starting switch, so that when the starting switch is closed the contacts I9 are closed, the function ofv the contacts 59 being to short circuit the barretter Ill during the preheating period which persists as. long as the starting switch is held in the closed position. On releasing the starting switch the contacts I], Na. and iii are opened so that the barretter is again in circuit to regulate the output of the accumulator. The starting switch 18 may be in-the form of a press button switch designed. tov cause simultaneous operation of. the. contacts I], ITa and i9.

Clearly, a further lamp may be actuated. from the reed I by adding thereto suitable movable contacts associated with appropriate fixed contacts for the respective transformer primary. Alternatively, the vibrator may control but. one

fluorescent lamp by utilising. the circuits described with reference tor the lamp. Li illustrated inthe accompanying diagrammatic drawing.

From the foregoing. it. will be observed thata accepts feature of the embodiments described is that the alternating current supplied to the fluores cent lamps provided by the respective transformers is separate and distinct in each case, although the storage battery supply and the vibrator is common to all the lamps, thereby the operation of any lamp in the arrangement described is independent and faults 'in a transformer or in a lamp are restricted in effect to the transformer and lamp affected.

Further, although in the embodiment described exactly similar lamps are referred to, clearly, the invention comprises the employment of lamps of different types or sizes, provided that appropriate transformers are designed to suit the operating conditions of the respective lamps. Although the use of a single barretter is described, the invention comprises the employment of a barretter in the supply line of each transformer, for example, in the accompanying diagram a barretter may be inserted between the line and the central tap of each transformer. In such cases provision will be made for short circuiting the barretters when the starter switch is operated to close the contacts such as IT, Ila.

By the present invention simple and effective operating means for fluorescent lamps in which the primary voltage is obtained from accumulators is achieved and a transportable unit may be provided adapted to receive the accumulator and the fluorescent lamps which unit comprises a housing for the accumulator, mountings for the lamps, and the necessary circuit connections and switches, and portability can in fact be obtained by employing accumulators of low voltage, for example 6 volt accumulators and consequently minimum weight, ease of maintenance (having in mind the necessary operation of topping the accumulator) and simplicity of construction is achieved.

When a lighting unit is to be used in coal mines the vibrator is in a sealed case, and it and the switch and the terminals of the fluorescent tube and connections are enclosed in a sealed case combined with the accumulator case. The accumulator may be arranged to be charged without removing its cover, because a joint of the size required for a multi-cell accumulator is liable to deteriorate with frequent opening and cease to be flameproof. For this purpose, flameproof vents are made from the space above the accumulator to atmosphere, through which gases generated during charge can escape. Further, the charging terminals may be made accessible outside the sealed casing, one at least being rendered inaccessible when the unit is in the mine, or being disconnected inside the casing from the accumulator.

The fluorescent tube or tubes are within the sealed case behind a glass forming part of the wall of the sealed case.

The transportable self-contained light unit comprises a casing of light metal consisting of a container provided with bosses 2| carrying a handle 22, and an upper portion or lid 23 which is attached to the container by screws 24. A suitable gasket (not shown) may be included between the container and lid to render the casing fiameproof when assembled. The container holds the accumulators 8, which may take the form of double cell units 25 in cases 26 of hard rubber or plastic. The plates 21 of the cells are attached in conventional manner to bars 28 which are joined to lugs 29 passing in gas-tight manner through the closures 30 of thermoplastic sealing a I of the cells are provided with tubes32, which are also sealed in the closure 30 and pass to openings 33 in resilient caps 34 held on the outside'of the container 20 by means of metal retaining members 35. Each cell is thus sealed from the inside of the casing and is vented to atmosphere'outside the casing, and may be recharged" insitu when the casing is closed. Straps 36 serve to connect serially cells of each accumulator and connections (not shown) are made from remaining lugs 29 to connect the accum'ulators in series. The outermost lugs of the accumulators may be connected to insulated sockoijzipbsinonb Vents a ets into which plugs carried by the lid 23 will fiton attachment of the lid to the container.

The lid 23 is provided with a rebated opening to receive a reflector 31, and a window 38, preferably of armour plate glass, which are retained in position by a metal frame 39 hearing on the window through the medium of a gasket 40. The frame'39 is attached to the lid by screws 4!. The lidis also provided with a shelf 42, to which are attached transformers 43, vibrator 44 (on a raised portion of the shelf) and brackets 45 having clips 46 to hold the fluorescent lamps LI and L2.

In openings in the upper wall of the lid 23 are fitted the main switch 9 and the starting switch 58. Suspended from the shelf 42 by means of screws 49 is a board of insulating material 50 serving to carry condensers 5| and resistances 52.

The raised portion of the shelf is sufiiciently high to allow the top of the vibrator 44 to protrude through an aperture in the upper wall of lid 23, and a cap 54 retained in position by screws 55 is provided to cover the aperture, a gasket 55 being included'between the flange of the cap and the wall of'the lid. The cap 54 allows of ready removal of the vibrator for replacement.

The accumulators are connected by way of the main switch 9, barretter (if used) and vibrator' 44 to the transformers 43 by connections arranged as shown in Fig. 1, and connections from the secondary windings of the said transformers to the fluorescent lamps LI and L2 and to the heater windings of the said lamps are provided as described above.

Charging terminals for the accumulators (not shown) are arranged to be accessible from the outside of the casing, one or both being adapted to be rendered inaccessible when the lighting unit is ready for use.

The above construction allows of a transportable lighting unit being produced with a weight of approximately 25 lbs. and a light output of substantially 13 lumens per lb. weight of the unit (assuming an overall efiiciency of 50 per cent). The unit may be recharged close to the coal face in mines by employing suitable charging stands.

Instead of producing alternating flow through the primary windings II, I la a pulsating individual flow can be produced as will be well understood in the art.

I claim:

1. A self-contained transportable electric lamp unit comprising a casing including a body portion and a cover portion having a window therein, means sealing said casing to render it flameproof, a re-chargeable battery in said body portion, vent means from said battery and opening through said body portion to atmosphere, a shelf in said cover portion, lamp supports on said shelf and having contacts for supporting a lamp behind said window, vibrator means on said primary windings of the two accaaaa shelf, a circuit connecting said vibrator means between said battery and said lamp Support contacts, and switch means on said casing and interposed in said circuit for actuating a lamp in said supports.

2. A self-contained transportable electric lighting unit comprising a casing including a body portion and a cover portion removably mounted on said body portion, a closed light transmitting window in said cover portion, means sealing said casing to render it flameproof, a rechargeable battery in said body portion, vent means from said battery and opening through said body portion to atmosphere, a shelf in said cover portion, a reflector in said cover portion, and mounted on said shelf behind said window, lamp support means including contacts and mounted on said shelf to support a lamp between said reflector and said window, vibrator means on said shelf behind said reflector, a circuit connecting said vibrator means between said battery and said lamp support contacts for energizing a lamp mounted in said lamp support means, and switch means on said casing and interposed in said circuit for actuating a: lamp in said support means:

3. A self-contained transportable electric lighting unit as defined in claim 2 wherein said cover portion is provided with an opening immediately adjacent said vibrator means for ready access thereto, and a closure removably sealed over said opening,

4'. A salt-contained transportable electric lighting unit comprising a casing including a body portion and a cover portion removably mounted on top of said body portion, a closed light-transmitting window in said cover portion, means sealing said casing to render it fiame proof, a rechargeable battery in said body portion, vent means. from said battery and opening through said body portion to atmosphere. a-

shelf in said cover portion, a reflector mounted on said shelf behind said window, lamp support means on said shelf, a pair of lamps supported by said lamp support means between said reflector and said window, said lamps being opstated at a higher voltage than that of said battery, a transformer for each lamp mounted on said shelf behind said reflector, a vibrator unit mounted behind said reflector and between said transformers, said vibrator unit being connected between said battery and both of said transformers and switch means connected between said battery and said vibrator means for controlling operation of said lamps.

5. A self-contained transportable electric lighting unit as defined in claim 4 wherein said cover portion has an opening and said vibrator unit extends through said opening, and a cap ren'rovably sealed to said cover portion around said; opening and enclosing said vibrator unit but permitting ready access thereto.

HAROLD AKROYD.

Reterences Cited in the file of this patent UNITED STATES PATENTS Number Name Date 13757589 Wheat May 6, 1930 33,964,201 Harsted' June 26, 1934 2,025,471 Osborne Dec. 24, 1935 2,057,660 Harrington Oct. 20, 1936 2,298,935 Freeman Oct. 13, 1942 2,318,536 Stern May 4, 1943 2,319,144 Lodge May 11, 1943 2,418,599 Beck Dec. 31, 1946 2,435,164 Sobel Jan. 27, I948 FOREIGN PATENTS Number Country Date 382,934 Great Britain- Nov. 3, 1932 449,810 Great Britain July 6, 1936' 633,793 Germany Aug. 6, 1936 

